Wellesley planners are drafting two cluster development measures aimed at preserving open space and diversifying the kinds of homes built in a community known for its plus-size mansions.

A cluster development calls for homes to be grouped more closely together than a traditional subdivision, allowing the same number of housing units on a property while leaving a larger area undeveloped, as contiguous open space.

Wellesley has had a provision for cluster development since the 1970s,  but it only applies to developments on at least 10-acre parcels, and has never been used, said Planning Director Meghan Jop.

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The Planning Board is planning to put two articles that would allow cluster developments before Town Meeting in April, Jop said.

The board’s Neighborhood Infill Cluster Development would apply to small subdivisions, involving two to four residential lots, and the Natural Resource Protection Cluster Development would cover subdivisions that would create five or more residential lots.

The number of lots allowed in the cluster developments would be the same as the number allowed in a traditional development of the same size.  

The warrant articles are still in draft form, Jop said, but the board will hold a public meeting on Jan. 14 to seek feedback. Cluster development is a goal outlined in the town’s comprehensive plan, she said.

The Natural Resource Protection Cluster would be mandatory  for any development of five or more lots, Jop said. It is being proposed in case one of Wellesley’s large institutions — such as Wellesley College, Babson College, or Massachusetts Bay Community College — decides to sell off a large tract of land.  The provision would keep big swaths of open space from being used for housing.

“A lot of them say they don’t intend to sell the land,” said Jop. “It’s a provision that might never be used.”

But the need to preserve wetlands, habitat, cultural landscapes, and open vistas is significant, she said, and without the Natural Resource Protection Cluster provision, a developer could do real damage to Wellesley’s landscape.

If there is conservation land such as wetlands in the parcel being developed, said Jop, developers can only count a fraction of it toward the land they are protecting. If, for example, 20 percent of the total parcel is wetlands, the protected space can only include 20 percent wetlands. This ensures that builders cannot just say they are protecting land they could not build on anyway.

The Neighborhood Infill Cluster would be an optional provision that would allow developers design flexibility.  

Last year saw a dramatic rise in construction of new single-family homes in town, according to Michael Grant, Wellesley’s inspector of buildings, with 72 new house permits issued compared with just 44 in 2011.

In 2007, citing an upward trend in home size and the growth of so-called McMansions, Town Meeting voters approved a large-house review provision that is based on the relationship between a home’s square footage and the size of its lot. Many new homes, Jop said, are built just below the large-house threshold to avoid the review process. Last year, she said, the town reviewed seven large homes, denying one. 

Cluster developments, she said, could present different options for construction.

Houses built in a cluster are often smaller and more affordable than those in traditional subdivisions, Jop said, although a developer could still build a 3,000-square-foot house in a cluster design, depending on the lot size.

The neighborhood cluster plan is not designed to favor affordable housing, she said. The town doesn’t require affordable housing in any development with fewer than five units. 

There are placeholders on the Town Meeting warrant for the two articles, said Jop.

In addition to the Jan. 14 public forum, there is a public zoning hearing planned for Feb. 4, she said. The Planning Board will decide after those meetings whether the articles are ready for Town Meeting.